Nitrogen Use Efficiency Of Different Rice Cultivars And The Effect Of Nitrogen And Zinc Interaction On Rice

Rice is the most important food crop in China.The rice production plays a very important role to protect China's food security.The application of nitrogen fertilizer is an important way to ensure the yield of rice.Zinc is an essential microelement which has a positive effect on rice yield and quality as well as the human health.In this study,five rice cultivars(Liangyoupeijiu,GD194,9311,7954 and Nipponbare)were grown under three different levels of nitrogen.The growth phenotype and nutrient content were analyzed at seedling stage,tillering stage and heading stage,respectively,in order to understand how rice response to the deficiency of nitrogen and identify the cultivars with high-and low-nitrogen use efficiency.In addition,both cultivars of high-and low-nitrogen use efficiency were grown under different nitrogen and zinc cross treaments to analyze the effects of nitrogen and zinc interaction on rice growth and seeding and its physiological mechanism.The main findings are as follows:1.Analysis of growth,nutrient uptake and nitrogen use efficiency of rice under differentnitrogen levelsFive rice cultivars were cultured at three nitrogen levels.The dry weight,plant height,root system structure,photosynthetic capacity and nutrient content of rice cultivars were analyzed at seedling stage,tillering stage and heading stage.The results showed that:(1)With the increased nitrogen supply level,significant promotions of plant height,dry weight,SPAD value and photosynthsis were observed at tillering stage and heading stage,while the total root length,total root surface area,total root volume and average diameter were significantly decreased.There were significant differences in the growth phenotype among the cultivars.The nitrogen use efficiency was significantly higher in Liangyoupeijiu than other four rice cultivars,and the lowest in Nipponbare.Ranking of five rice cultivars in growth phenotype is as follows: Liangyoupeijiu>GD194?9311?7954> Nipponbare.(2)With the increased nitrogen supply level,the nitrogen accumulation increased continuesly.Liangyoupeijiu has the highest and Nipponbare has the lowest nitrogen accumulation.The physiological nitrogen utilization efficiency and nitrogen use index of Liangyoupeijiu were significantly higher than those of other cultivars.When compared to other cultivars,under 0.48 mmol/L and 0.96 mmol/L N condtitions,the shoot nitrogen useefficiency increased by 13%-37% and 24%-50% at tillering stage and increased by24%-80% and 44%-66% at heading stage.Results showed that Liangyoujuji was a nitrogen efficient cultivar,and Nipponbare was a nitrogen inefficient cultivar.Therefore,these two cultivars were used for the subsequent study of nitrogen and zinc interaction.(3)In addition,the increased nitrogen level promoted the growth and development of rice and increased the accumulation of phosphorus and zinc in the shoots of each rice cultivar.At tillering stage and heading stage,the distribution of phosphorus of each rice variety was decreased in root and increased in shoot by 2.9%-11.1% and 3.4%-15%,respectively.At seedling stage,with the increased nitrogen levels,there was no significant difference in zinc concentration and accumulaton.At tillering stage and heading stage,the increased nitrogen level promoted the content of zinc in root and new leaves,decreased the content of zinc in stem,but promoted the transfer of zinc from root and stem to leaves in rice.2.The growth phenotype,yield and nutrient variation of high-and low-nitrogen use efficiency cultivars under nitrogen and zinc cross treatment.(1)Two rice cultivars were cultured under different nitrogen gradients or zinc gradients to analyze the growth phenotype and nutrient contents.The results showed that:(1)Under different nitrogen gradients,the increased nitrogen level promoted plant growth and development,but excessive nitrogen also inhibited plant growth.The increased nitrogen level could improve the accumulation of nitrogen,phosphorus,potassium and zinc in the two rice cultivars.The suitable nitrogen level promoted the transfer of phosphorus and potassium from rice root to shoot,and promoted the distribution of zinc from stem to new leaves.(2)Under different zinc gradients,the increased zinc level promoted plant growth and development,but excessive zinc also inhibited plant growth.The inefficient cultivar was more sensitive to high nitrogen or high zinc level than the efficient one.With the increased zinc level,the nitrogen concentration in root was increased while differed in other parts.The appropriate zinc level can increase the nitrogen distribution ratio in the new leaf.In a certain range,the zinc level decreased phosphorus content but promoted the potassium content in various parts of rice.Therefore,the optimum nitrogen and zinc levels were obtained for the subsequent study on the interaction of nitrogen and zinc.(2)The effects of nitrogen and zinc interaction on the growth and nutrient contents of rice were studied in high-and low-nitrogen use efficiency cultivars Liangyoupeijiu andNipponbare.Under both normal and low nitrogen levels,the addition of zinc significantly increased the plant height and dry weight of the two cultivars,and the effect was more significant under low nitrogen conditions.Application of zinc could promote the nitrogen use efficiency.Under the normal nitrogen level,the addition of zinc increased the root nitrogen concentration and the uptake and accumulation of nitrogen in the tissues,and promoted the transfer of nitrogen to the leaves.Under the condition of two zinc levels,the increased level of nitrogen promoted the growth and development of rice and the distribution and accumulation of zinc in leaves.At the same time,increased nitrogen level promoted the plant phosphorus and potassium uptake and the addition of zinc promoted the accumulation of phosphorus and potassium in the plant.At the high nitrogen level,the addition of zinc significantly increased the activity of glutamine synthetase in the tissues and promoted the fixation of rice nitrogen.(3)The yield and constituent factors of rice and the nutrient contents of each tissue were analyzed in the high-and low-nitrogen use efficiency cultivars Liangyoupeijiu and Nipponbare in the field assay under the nitrogen and zinc cross treatments.The results showed that the application of nitrogen fertilizer and zinc fertilizer could promote the dry weight in different parts of rice,the plant and theoretical yield.After the zinc fertilizer application,the yield per plant of Liangyoupeijiu was increased by 22%,37% and 10%under the conditions of low,medium and high nitrogen(90 kg/hm2,180 kg/hm2,270kg/hm2),respectively;the theoretical yield of Liangyoupeijiu was increased by 21% and13% under the middle and high nitrogen conditions,respectively.The plant yield of Nipponbare was increased by 80% and 35% and the theoretical yield was increased by63% and 38% under the middle and high nitrogen conditions,respectively.There was no significant difference in the plant yield between the condition of low nitrogen adding zinc and medium nitrogen without zinc.There was no significant difference in the theoretical yield between the condition of medium nitrogen adding zinc and high nitrogen without zinc.Therefore,the application of zinc fertilizer significantly increased the yield of rice.The application of zinc fertilizer under low or medium nitrogen level can reach to the similar yield of plants grown under high nitrogen level.Thereafter,it is possible to reduce the nitrogen fertilizer without reducing the yield production during the agricultural activities.Furthermore,the application of zinc fertilizer could promote the accumulation of nitrogen and the nitrogen distribution ratio in the shoot.The addition of zinc fertilizer under high nitrogen condition could promote the nitrogen concentration in different partsof rice.The effect of nitrogen fertilizer on the increase of zinc concentrations in different parts of rice was different in cultivars,but it could promote the accumulation of zinc in various parts and increase the distribution ratio of zinc in old leaves,new leaves and leaf sheath.At the same time,the increase of nitrogen level could promote the phosphorus and potassium concentrations and the accumulation amount.The zinc applying reduced the phosphorus concentration and accumulation in different parts of Nipponbare as well as the phosphorus concentration of Liangyoupeijiu.